A 72-year-old woman with a history of rheumatoid arthritis and chronic obstructive pulmonary sought care for a 3-month history of progressive difficulty walking on uneven terrain and climbing stairs. In the 2 preceding weeks, she also noted difficulty standing up from a seated position. She reported no sensory symptoms but recently noticed dry mouth and new-onset constipation with decreased appetite. Electromyography showed diffusely low-amplitude compound muscle action potential responses to single-nerve stimuli at rest, with normal sensory nerve action potentials. Studies of the ulnar and femoral motor nerves demonstrated a decrement to low-frequency repetitive stimulation (12%) and substantial postexercise facilitation (200%) and decrement repair. The serum was positive for cyclic citrullinated peptide antibody, rheumatoid factor, and P/Q-type voltage-gated calcium channel antibody. Computed tomography of the chest showed subcarinal and right hilar lymphadenopathy without evidence of a primary lesion, with avidity on 18F-fludeoxyglucose–positron emission tomography/computed tomography. Transbronchial fine-needle aspiration biopsy of the lymph node revealed small cell lung carcinoma. The patient was diagnosed with Lambert-Eaton myasthenic syndrome and small cell lung carcinoma. Concurrent chemotherapy and radiation were administered for the small cell lung carcinoma, with some improvement of the patient’s weakness. Symptomatic treatment for Lambert-Eaton myasthenic syndrome was initiated. Therapy with 3,4-diaminopyridine improved the patient’s weakness, but her daily activities were limited by persistent, moderate, lower extremity weakness. The weakness objectively improved with intravenous immunoglobulin therapy. Two years later, the patient was maintained on 3,4-diaminopyridine and monthly intravenous immunoglobulin, with minimal persistent weakness and no evidence of cancer recurrence. Lambert-Eaton myasthenic syndrome was first described at Mayo Clinic in 1956 as a “myasthenic syndrome associated with malignant tumors” that had characteristic electromyographic findings, later shown to be presynaptic by microelectrophysiologic testing.
A Case of Small Cell Lung Carcinoma with SIADH and Lambert-Eaton Myasthenic Syndrome.
